Texas Instruments SR-51-II ... a more complex calculator than you think

Thursday, November 7, 2013, 11:00 PMPosted by Administrator

This was a mixture between an older SR-51A and the later TI-55, it's inner electronics is more complex than comparable other TI models of the same decade.My own one is working, but in a less desirable condition, around the power switch, painting is already gone. Also, I had to open it because the display was not fitted correctly (see second picture how to open).

How to open... somewhat tricky, also because the plastic material is a bit brittle.

Do you remember the time a scientific calculator was (very) expensive ?I am not really a collector of these vintage calculators, but some are very interesting and also unique. The first mass production LED display based calculator was the Texas Instruments Datamath 2500, and luckily I own also one (which I bought at Ebay a few years ago, still not too expensive).Later, many real famous models (also from HP) were sold, e.g. the TI-57, TI-58C and the Rolls Royce of these all, the TI-59 with magnetic stripe reader.In the next time, I will introduce some here, starting with the TI-45, which was not too common also because it has a green VFD (Vacuum Fluorescent Display),This one has basically a set of common scientific functions, but can't be programmed.The calculator case is comparable to the cases of the TI-57/58/59 series.For me, it's a very beautiful one (due to the green display).Unfortunately most of the time you buy nowadays such a vintage calculator, the battery pack is destroyed by battery acid (from the NiCD cells).For these who are looking for a replacement, take a look >here<.

There will be something new I didn't expected... a new device was developed from Jim Drew (he already developed a lot of cool gadgets for the Commodores), which may supersede the Kryoflux device (you know it - the magic pcb/box which could read almost every floppy disk format).

It's much better than the Kryoflux:It uses a 25ns capture resolution, where Kryoflux uses a 41.66ns resolution.So, copies and images made with SuperCard Pro will be much more exact.

I own an old but beautiful Intel 486 based notebook, a Siemens PCD-4ND with a build-in floppy drive (a Citizen W1D). This drive is removable.

Unfortunately the floppy drive is not working reliable enough anymore.So I had the idea to repair it, and I had to open it:

You have to remove the plasic case (fixed with 2 screws), then a metal sheet (fixed with 4 very small screws)...

... and you can recognize now a missing tension for the belt:

To get the belt out of the drive, you have to lift the motor also (2 screws).The dimensions of the belt are: 220mm circumference (110mm x2, as shown in the picture below, that means a diameter of 70mm), 1mm width and far less then 1mm thickness.

As you can see, I marked a red dot in the third picture, may be I can place there a small bumper to increase the tension of the (old) belt.

I have NO IDEA where to get such a belt. Seems to be very difficult.If someone has an idea where to get such a plastic belt, let me know, thanks in advance.Others already looked for some and had no success (see related link)...